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    <h1 class="post-title" itemprop="name">
      YzmCMS-V5.4 后台Getshell
    </h1>
  

	<div class='post-body mb'>
		<h1 id="YzmCMS-V5-4-后台Getshell"><a href="#YzmCMS-V5-4-后台Getshell" class="headerlink" title="YzmCMS-V5.4 后台Getshell"></a>YzmCMS-V5.4 后台Getshell</h1><h3 id="代码审计"><a href="#代码审计" class="headerlink" title="代码审计"></a>代码审计</h3><blockquote>
<p>漏洞文件：yzmphp\core\class\cache_file.class.php</p>
</blockquote>
<ul>
<li>代码171-179行,使用了file_put_contents(),其中<code>$file</code>和<code>$contents</code>可控</li>
</ul>
<pre><code class="php">protected function _fileputcontents($file, $contents){
    if($this-&gt;config[&#39;mode&#39;] == 1){
        $contents = serialize($contents);
    }else{
        $contents = &quot;&lt;?php\nreturn &quot;.var_export($contents, true).&quot;;\n?&gt;&quot;;
    }

    $filesize = file_put_contents($file, $contents, LOCK_EX);
    return $filesize ? $filesize : false;
}</code></pre>
<ul>
<li>我们继续跟进<code>_fileputcontents()</code>,在同一文件代码62-75行调用了该方法，我们继续跟进<code>set()</code></li>
</ul>
<p><img src="https://www.mycute.cn/static/umeditor/php/upload/20191215/1576413364302.png" alt="img"></p>
<blockquote>
<p>漏洞文件：yzmphp\core\function\global.func.php</p>
</blockquote>
<ul>
<li><code>global.func.php</code>的1017-1021中的<code>setcache()</code>方法疑似调用了<code>set()</code>方法,并且<code>$name, $data, $timeout</code>均可控，我们跟进<code>load_sys_class(&#39;cache_factory&#39;,&#39;&#39;,0);</code>看看<code>get_instance()-&gt;get_cache_instances()</code>到底调用了哪个文件。</li>
</ul>
<p><img src="https://www.mycute.cn/static/umeditor/php/upload/20191215/15764136241676.png" alt="img"></p>
<blockquote>
<p>漏洞文件：\yzmphp\core\class\cache_factory.class.php</p>
</blockquote>
<ul>
<li>很明显<code>C(&#39;cache_type&#39;)</code>决定了他调用哪个文件中的<code>set()</code>方法，我们跟进<code>cache_type</code></li>
</ul>
<p><img src="https://www.mycute.cn/static/umeditor/php/upload/20191215/15764138453674.png" alt="img"></p>
<ul>
<li>跟进发现在<code>common\config\config.php</code>做了定义，<code>cache_type</code>默认使用<code>file</code>，<code>mode</code>存在两种模式，我们选择<code>1</code>-序列化看看或许可能读取缓存存在反序列化的可能。那么回头看他默认使用<code>file</code>也就是调用了<code>cache_file.class.php</code>所以我们的猜测没错。同时这里还是用了<code>file_config</code>这个参数，我们继续跟进<code>setcache()</code>方法</li>
</ul>
<p><img src="https://www.mycute.cn/static/umeditor/php/upload/20191215/15764140583404.png" alt="img"></p>
<blockquote>
<p>漏洞文件：\common\function\system.func.php</p>
</blockquote>
<ul>
<li>这里$modelinfo是从数据库中得到所以可控，$filename指定了名称<code>modelinfo</code>或者<code>modelinfo_all</code>。我们继续跟进<code>get_modelinfo()</code>会发现都不传入参数，所以默认$typeall = 0,也就是说文件名称固定<code>modelinfo</code></li>
</ul>
<p><img src="https://www.mycute.cn/static/umeditor/php/upload/20191215/15764172002656.png" alt="img"></p>
<ul>
<li>我们再回到<code>yzmphp\core\class\cache_file.class.php</code>,发现文件名称和路径由<code>_file()</code>方法决定。而<code>$id</code>正是我们传入的。我们跟进<code>_file()</code>方法</li>
</ul>
<p><img src="https://www.mycute.cn/static/umeditor/php/upload/20191215/15764175738040.png" alt="img"></p>
<ul>
<li>我们可以得知filename是由config[‘cache_dir’] 和传入的<code>$id</code>和<code>config[&#39;suffix&#39;]</code>拼接而成。我们再看<code>config[&#39;suffix&#39;]</code>和<code>&#39;cache_dir&#39;</code>是什么?</li>
</ul>
<p><img src="https://www.mycute.cn/static/umeditor/php/upload/20191215/15764216664657.png" alt="img"></p>
<ul>
<li>我们在审计<code>common\config\config.php</code>时候已经发现这里定义了<code>file_config</code>,这样我们就完整知道缓存文件写在<code>cache/chche_file/modelinfo.cache.php</code></li>
</ul>
<p><img src="https://www.mycute.cn/static/umeditor/php/upload/20191215/15764216283148.png" alt="img"></p>
<ul>
<li>而且这里是模型的缓存，我们直接到后台写入一个php代码看看。</li>
</ul>
<p><img src="https://www.mycute.cn/static/umeditor/php/upload/20191215/1576421587721.png" alt="img"></p>
<ul>
<li>需要访问前台让其生成新的缓存文件。我们打开：<code>cache/chche_file/modelinfo.cache.php</code>看看</li>
</ul>
<p><img src="https://www.mycute.cn/static/umeditor/php/upload/20191215/15764187209911.png" alt="img"></p>
<ul>
<li>我们访问<code>http://域名/cache/chche_file/modelinfo.cache.php</code>看看，成功getshell<br> <img src="https://www.mycute.cn/static/umeditor/php/upload/20191215/15764196355940.png" alt="img"></li>
</ul>
<hr>
<h3 id="后记"><a href="#后记" class="headerlink" title="后记"></a>后记</h3><ul>
<li>如果<code>mode</code>选择的模式是2的话是无法getshell的，由于<code>var_export()</code>进行了转义，暂时没有找到方法，但是该cms默认的是选择<code>2</code>导致这个漏洞有点鸡肋。</li>
</ul>

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		<time class="post-date" datetime="2019-12-15T14:12:56.000Z" itemprop="datePublished">2019-12-15</time>
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